1. Field of the Invention
This invention relates to a device for measuring water flow rate in plant stem. More particularly, the invention relates to a device for measuring water flow rate in the stem of a plant in an on-line real time fashion.
2. Related Art Statement
In the field of growing plants in green houses or the like facilities, it is desirable to effect reasonable water control, automatic irrigation and monitoring of plant conditions. To this end, accurate quantitative knowledge is necessary on the water flow rate in the plant stem. The stem water flow represents water absorption by roots for compensation of the transpiration at leaves. Accordingly, there is a pressing need for development of a device for measuring the water flow rate in plant stem on the basis of on-line real time operation.
Heretofore, a heat pulse method is known for measuring the water flow rate in the plant stem, for instance as disclosed in the Journal of Botanical Society of Federal Republic of Germany, issued in 1937, volume 55, pages 514-529. This known method measures the propagation velocity of heat pulses in a plant stem, and it is useful in evaluating relative strength of water flow in the plant stem.
Another known approach to the measuring of water flow rate in the plant stem is a stem heat balance method which is disclosed for instance in the Journal of Institute of Agricultural Meteorology, issued in 1981, volume 37, pages 9-17. In this known method, a certain quantity of heat is continuously applied to a portion of plant stem, and the water flow rate in the plant stem is determined based on the heat balance in response to such heat application. With this stem heat balance method, the absolute value of the water flow rate in plant stem can be directly measured.
However, the heat pulse method has a shortcoming in that, although being effective in evaluating relative intensity of water flow in plant stem, it cannot measure the absolute value of the water flow in plant stem.
Further, continuous measurement is not possible with it. Thus, the heat pulse method is not suitable for quantitative analysis of the water flow in plant stem.
The stem heat balance method has a shortcoming in that, although it can measure the absolute value of water flow rate in plant stem, its process for measurement and calculation is complicated because accurate measurements are required on a number of ever changing items of the heat balance. Further, each item of the heat balance can be determined only by cutting the plant stem for additional measurement, so that this method is not suitable for on-line real time data processing of the water flow rate in plant stem.